This proposal outlines a research program for the purification and study of the structures of guanine aminohydrolases from brain, liver and kidney. Purification and separation of the distinct forms of guanine aminohydrolase will be accomplished by using affinity chromatography on 9-(p-aminoethoxyphenyl)guanine sepharose and isoelectric focusing. Purity will be assessed by using polyacrylamide gel electrophoresis and gel isoelectric focusing experiments. Molecular weights will be determined by gel chromatography, ultracentrifugation and gel electrophoresis experiments. Subunit structure will be studied by chromatography in the presence of denaturing agents and by gel electrophoresis in the presence of SDS. Amino acid end group analysis will provde additional information about the subunits. Kinetic parameters for each enzyme form will be determined with respect to pH, temperature and allosteric response to guanine nucleotides. Substrate specificities will be studied by using a variety of purine substrates. The information generated by the proposed study will provide insight into some of the factors which affect the activity of guanine aminohydrolase and may lead to a better understanding of its role in the metabolism of guanine and in the regulation of purine metabolism.